All About Tequila and Mezcal

All Tequila is Mezcal, but not all Mezcal is Tequila. —Tequila marketing mantra

Tequila, and its country cousin Mezcal, are made by distilling the fermented juice of agave plants in Mexico. The agave is a spiky-leafed member of the lily family (it is not a cactus) and is related to the century plant. By Mexican law the agave spirit called Tequila can be made only from one particular type of agave, the blue agave (Agave Tequiliana Weber), and can be produced only in specifically designated geographic areas, primarily the state of Jalisco in west-central Mexico.

Mezcal is made from the fermented juice of other species of agave. It is produced throughout most of Mexico. Both Tequila and Mezcal are prepared for distillation in similar ways. The agave, also know as maguey (pronounced muh-GAY), is cultivated on plantations for eight to 10 years, depending on the type of agave. When the plant reaches sexual maturity it starts to grow a flower stalk. The agave farmer, or campesino, cuts off the stalk just as it is starting to grow. This redirects the plant growth into the central stalk, swelling it into a large bulbous shape that contains a sweet juicy pulp. When the swelling is completed, the campesino cuts the plant from its roots and removes the long sword-shaped leaves, using a razor-sharp pike-like tool called a coa. The remaining piña ("pineapple"—so-called because the cross-thatched denuded bulb resembles a giant green and white pineapple) weighs anywhere from 25 to 100 pounds.
At the distillery the piñas are cut into quarters. For Tequila they are then slowly baked in steam ovens or autoclaves (oversized pressure cookers) until all of the starch has been converted to sugars. For Mezcal they are baked in underground ovens heated with wood charcoal (which gives Mezcal its distinctive smoky taste). They are then crushed (traditionally with a stone wheel drawn around a circular trough by a mule) and shredded to extract the sweet juice, called aguamiel (honey water).
The fermentation stage determines whether the final product will be 100 percent agave or mixed ("mixto"). The highest-quality Tequila is made from fermenting and then distilling only agave juice mixed with some water. Mixto is made by fermenting and then distilling a mix of agave juice and other sugars, usually cane sugar with water. Mixtos made and bottled in Mexico can contain up to 40% alcohol derived from other sugars. Mixtos that have been shipped in bulk to other countries for bottling (primarily the United States) may have the agave content further reduced to 51% by the foreign bottler. By Mexican law all 100% agave or aged Tequila must be bottled in Mexico. If a Tequila is 100 percent agave it will always say so on the bottle label. If it doesn't say 100% it is a mixto, although that term is seldom used on bottle labels.

Source: Tastings.com